
At each system element, the shields of its communication bus cables must be tied together. If the communication bus is entirely within one building, the resulting continuous shield must be connected to a ground at one point only. If the commu- nication bus cable exits from one building and enters another, the shields must be connected to grounds at the lightning suppressor in each building where the cable enters or exits the building (one point per building only). To connect the unit to the network:
1.Turn off power to the control box.
2.Cut the SCN wire and strip the ends of the red (+), white (ground), and black
3.Connect the red wire to (+) terminal on TB3 of the plug, the white wire to COM terminal, and the black wire to the
4.The RJ14 SCN connector on TB3 can also be used, but is only intended for temporary connection (for example, a laptop computer running Service Tool).
IMPORTANT: A shorted SCN bus cable will prevent some routines from running and may prevent the unit from start- ing. If abnormal conditions occur, unplug the connector. If conditions return to normal, check the SCN connector and cable. Run new cable if necessary. A short in one section of the bus can cause problems with all system elements on the bus.
Table 2 — Thermistor Designations
THERMISTOR | PIN |
| ||
CONNECTION | THERMISTOR INPUT | |||
NO. |
| |||
| POINT |
| ||
|
|
| ||
T1 |
| Cooler Leaving Fluid | ||
T2 |
| Cooler Entering Fluid | ||
T7 |
| Circuit A Return Gas | ||
|
| Temperature (Accessory) | ||
|
|
| ||
T8 |
| Circuit B | ||
|
| Gas Temperature (Accessory) | ||
|
|
| ||
T9 |
| |||
|
| Sensor | ||
|
|
| ||
T10 |
| Accessory Remote Space | ||
| Temperature Sensor or | |||
|
|
| Dual LWT Sensor | |
| LEGEND |
| ||
LWT — Leaving Water Temperature |
| |||
MBB — Main Base Board |
|
Table 3 — Status Switches
STATUS | PIN CONNECTION |
SWITCH | POINT |
Chilled Water Pump 1 | |
Chilled Water Pump 2 | |
Remote On/Off | |
Cooler Flow Switch | |
Compressor Fault Signal, A1 | |
Compressor Fault Signal, A2 | |
Compressor Fault Signal, B1 | |
Compressor Fault Signal, B2 |
Table 4 — Output Relays
RELAY | DESCRIPTION | |
NO. | ||
| ||
K1 | Energize Compressor A1 | |
Energize Compressor A1 and Condenser Fan A1 | ||
| ||
K2 | Energize Compressor B1 and Condenser Fan B1 at Low | |
Speed | ||
| Energize Compressor B1 and Condenser Fan B1 | |
K3 | Energize Chilled Water Pump 1 Output | |
K4 | Energize Chilled Water Pump 2 Output | |
K5 | Energize Compressor A2 (all but 010, 015 60Hz) | |
K6 | Energize Compressor B2 | |
K7 | Alarm Relay | |
K8 | Cooler/Pump Heater | |
K9 | Energize Condenser Fan at Low Speed | |
Energize Condenser Fan A1 | ||
| Energize Condenser Fan A2 | |
| Energize Condenser Fan at High Speed | |
K10 | Energize Condenser Fan A2 | |
Energize Condenser Fan B1 at High Speed | ||
| ||
| Energize Condenser Fan B2 | |
K11 | Minimum Load Valve |
Table 5 — SCN Communication Bus Wiring
MANUFACTURER | PART NO. | ||
Regular Wiring | Plenum Wiring | ||
| |||
Alpha | 1895 | — | |
American | A21451 | A48301 | |
Belden | 8205 | 884421 | |
Columbia | D6451 | — | |
Manhattan | M13402 | M64430 | |
Quabik | 6130 | — |
OPERATING DATA
Sensors — The electronic control uses 3 to 6 thermistors to sense temperatures for controlling chiller operation. See Table 2. These sensors are outlined below. Thermistors T1, T2, T9 and accessory suction gas temperatures (T7,T8) are 5 kΩ at 77 F (25 C) and are identical in temperature versus resistance and voltage drop performance. Thermistor T10 is 10 kΩ at 77 F (25 C) and has a different temperature vs. resistance and voltage drop performance. See Thermistors section for
T1 — COOLER LEAVING FLUID SENSOR — On 30RA010- 030 sizes, this thermistor is installed in a friction fit well at the bottom of the
T2 — COOLER ENTERING FLUID SENSOR
T7,T8 — COMPRESSOR RETURN GAS TEMPERA- TURE SENSOR (ACCESSORY) — A well for this sensor is factory installed in each circuit's suction line. If desired, a 5 kΩ thermistor (Sterling part number HH79NZ029) can be installed in this well and connected to the Main Base Board as shown in Table 2. Use the Scrolling Marquee display to con- figure the sensor (Configuration mode,
T9 —
4